JP6468291B2 - Silicon carbide epitaxial substrate, silicon carbide epitaxial substrate manufacturing method, and silicon carbide semiconductor device manufacturing method - Google Patents

Description

  The present disclosure relates to a silicon carbide epitaxial substrate and a method for manufacturing a silicon carbide semiconductor device. This application claims priority based on Japanese Patent Application No. 2015-179559, which is a Japanese patent application filed on September 11, 2015, and incorporates all the content described in the Japanese patent application. .

  Japanese Patent Laying-Open No. 2014-170891 (Patent Document 1) discloses a method of forming a silicon carbide layer on a silicon carbide single crystal substrate by epitaxial growth.

JP 2014-170891 A

  A silicon carbide epitaxial substrate according to the present disclosure includes a silicon carbide single crystal substrate and a silicon carbide layer. The silicon carbide single crystal substrate includes a first main surface. The silicon carbide layer is on the first main surface. The silicon carbide layer includes a second main surface opposite to the surface in contact with the silicon carbide single crystal substrate. The maximum diameter of the second main surface is 100 mm or more. A linear orientation flat is provided on the silicon carbide single crystal substrate and the silicon carbide layer. The silicon carbide layer has a central region, a first end region, and a second end region. The central region is at a position 2 μm away from the center of the second main surface toward the first main surface in a direction perpendicular to the second main surface. The first end region is located on a plane that bisects the orientation flat vertically and is 1 mm away from the orientation flat toward the central region when viewed from the direction perpendicular to the second main surface. is there. The second end region is a direction rotated 90 ° counterclockwise from the first end region as viewed from the central region, and is 1 mm away from the outer edge of the silicon carbide layer toward the central region. In position. The thickness of the silicon carbide layer is 5 μm or more. The first ratio of the absolute value of the difference between the dopant density in the first end region and the dopant density in the central region with respect to the average value of the dopant density in the first end region and the dopant density in the central region is 40% or less. is there. The second ratio of the absolute value of the difference between the dopant density in the second end region and the dopant density in the central region with respect to the average value of the dopant density in the second end region and the dopant density in the central region is 40% or less. is there.

FIG. 1 is a schematic plan view showing the configuration of the silicon carbide epitaxial substrate according to the present embodiment. FIG. 2 is a schematic plan view showing a carrier concentration measurement position. 3 is a schematic cross-sectional view taken along the line III-III in FIG. 4 is a schematic cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a partial schematic cross-sectional view showing the configuration of the silicon carbide epitaxial substrate manufacturing apparatus according to the present embodiment. FIG. 6 is a partial schematic cross-sectional view showing the configuration of the susceptor plate of the silicon carbide epitaxial substrate manufacturing apparatus according to this embodiment. FIG. 7 is a schematic plan view showing the configuration of the gas ejection holes of the silicon carbide epitaxial substrate manufacturing apparatus according to the present embodiment. FIG. 8 is a schematic plan view showing the configuration of the first example of the susceptor plate of the silicon carbide epitaxial substrate manufacturing apparatus according to this embodiment. FIG. 9 is a schematic plan view showing the configuration of the second example of the susceptor plate of the silicon carbide epitaxial substrate manufacturing apparatus according to this embodiment. FIG. 10 is a flowchart schematically showing a method for manufacturing the silicon carbide semiconductor device according to this embodiment. FIG. 11 is a schematic cross-sectional view showing a first step of the method for manufacturing the silicon carbide semiconductor device according to this embodiment. FIG. 12 is a schematic cross-sectional view showing a second step of the method for manufacturing the silicon carbide semiconductor device according to this embodiment. FIG. 13 is a schematic cross-sectional view showing a third step of the method for manufacturing the silicon carbide semiconductor device according to this embodiment.

[Description of Embodiment of Present Disclosure]
First, an embodiment of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description is not repeated. In the crystallographic description of the present specification, the individual orientation is indicated by [], the collective orientation is indicated by <>, the individual plane is indicated by (), and the collective plane is indicated by {}. A negative crystallographic index is usually expressed by adding a “-” (bar) above the number, but in this specification the crystallographic index is indicated by a negative sign in front of the number. Represents the negative exponent above.

  (1) A silicon carbide epitaxial substrate 100 according to the present disclosure includes a silicon carbide single crystal substrate 10 and a silicon carbide layer 20. Silicon carbide single crystal substrate 10 includes a first main surface 11. Silicon carbide layer 20 is on first main surface 11. Silicon carbide layer 20 includes a second main surface 30 opposite to surface 14 in contact with silicon carbide single crystal substrate 10. The maximum diameter of the second main surface 30 is 100 mm or more. Linear orientation flat 5 is provided on silicon carbide single crystal substrate 10 and silicon carbide layer 20. Silicon carbide layer 20 has a central region 33, a first end region 31, and a second end region 32. The central region 33 is located 2 μm away from the center 35 of the second main surface 30 toward the first main surface 11 in the direction perpendicular to the second main surface 30. The first end region 31 is located on a plane that bisects the orientation flat 5 in the vertical direction when viewed from the direction perpendicular to the second main surface 30, and is directed from the orientation flat 5 toward the central region 33. 1 mm away. The second end region 32 is a direction rotated 90 ° counterclockwise from the first end region 31 when viewed from the central region 33, and from the outer edge 34 of the silicon carbide layer 20 to the central region 33. 1 mm away from Silicon carbide layer 20 has a thickness of 5 μm or more. The first ratio of the absolute value of the difference between the dopant density of the first end region 31 and the dopant density of the central region 33 with respect to the average value of the dopant density of the first end region 31 and the dopant density of the central region 33 is: 40% or less. The second ratio of the absolute value of the difference between the dopant density of the second end region 32 and the dopant density of the central region 33 with respect to the average value of the dopant density of the second end region 32 and the dopant density of the central region 33 is: 40% or less.

  When forming the silicon carbide layer by epitaxial growth, the silicon carbide layer is formed on the silicon carbide single crystal substrate while rotating the silicon carbide single crystal substrate. Therefore, even if the concentration of the source gas (including the dopant gas) on the silicon carbide single crystal substrate is not uniform, the silicon carbide single crystal substrate rotates, so silicon carbide formed on the silicon carbide single crystal substrate. It is believed that the dopant density in the layer is averaged. However, in practice, the dopant density tends to be higher in the outer peripheral region than in the central region of the silicon carbide layer.

  The inventors examined the cause of the higher dopant density in the outer peripheral region than in the central region of the silicon carbide layer. As a result, it was found that the disturbance of the flow of the source gas is one of the causes. Specifically, the flow of the source gas is disturbed by the source gas entering the gap between the side surface of the recess provided in the susceptor plate and the side surface of the silicon carbide single crystal substrate disposed in the recess. It is thought that there is. In addition, it is considered that the flow of the source gas flowing on the silicon carbide single crystal substrate is disturbed because the thickness of the silicon carbide single crystal substrate is smaller than the depth of the concave portion. It is considered that the dopant density in the outer peripheral region becomes higher than the dopant density in the central region when the flow of the source gas is disturbed near the outer periphery of the silicon carbide single crystal substrate.

  Further, it is considered that one of the causes is that the electric field concentrates at the outer peripheral corner of the susceptor plate. Specifically, when the susceptor plate is heated by induction heating, the electric field concentrates on the outer peripheral corner of the susceptor plate. Therefore, the temperature of the outer peripheral corner portion of the susceptor plate is higher than the temperature of other portions of the susceptor plate. Therefore, the temperature of the outer peripheral region of the silicon carbide single crystal substrate close to the outer peripheral corner is higher than the temperature of the central region. As a result, the dopant density in the outer peripheral region is considered to be higher than the dopant density in the central region.

  Based on the above findings, the inventors configured the susceptor plate as described below. Thereby, disturbance of the flow of the source gas on the silicon carbide single crystal substrate can be suppressed. Moreover, the influence of the electric field concentration at the outer peripheral corner of the susceptor plate with respect to the silicon carbide single crystal substrate can be suppressed. As a result, the difference between the dopant density in the central region and the dopant density in the outer peripheral region can be reduced.

  (2) In silicon carbide epitaxial substrate 100 according to (1) above, the first ratio may be 30% or less.

  (3) In silicon carbide epitaxial substrate 100 according to (2) above, the first ratio may be 20% or less.

  (4) In silicon carbide epitaxial substrate 100 according to any of (1) to (3) above, the second ratio may be 30% or less.

  (5) In silicon carbide epitaxial substrate 100 according to (4) above, the second ratio may be 20% or less.

  (6) In silicon carbide epitaxial substrate 100 according to (1) above, the maximum diameter may be 150 mm or more.

  (7) A method for manufacturing silicon carbide semiconductor device 300 according to the present disclosure includes the following steps. Silicon carbide epitaxial substrate 100 according to any one of (1) to (6) above is prepared. Silicon carbide epitaxial substrate 100 is processed.

[Details of Embodiment of the Present Disclosure]
Hereinafter, an embodiment of the present disclosure (hereinafter also referred to as “the present embodiment”) will be described. However, this embodiment is not limited to these.

(Silicon carbide epitaxial substrate)
As shown in FIGS. 1 to 4, silicon carbide epitaxial substrate 100 according to the present embodiment has a silicon carbide single crystal substrate 10 and a silicon carbide layer 20. Silicon carbide single crystal substrate 10 includes a first main surface 11 and a third main surface 13 opposite to the first main surface 11. Silicon carbide layer 20 includes a fourth main surface 14 in contact with silicon carbide single crystal substrate 10 and a second main surface 30 opposite to fourth main surface 14. As shown in FIG. 1, silicon carbide epitaxial substrate 100 may have an orientation flat 5 extending in first direction 101. Silicon carbide epitaxial substrate 100 may have a second flat (not shown) extending in second direction 102. The first direction 101 is, for example, the <11-20> direction. The second direction 102 is, for example, the <1-100> direction.

  Silicon carbide single crystal substrate 10 (hereinafter may be abbreviated as “single crystal substrate”) is composed of a silicon carbide single crystal. The polytype of the silicon carbide single crystal is, for example, 4H—SiC. 4H—SiC is superior to other polytypes in terms of electron mobility, dielectric breakdown field strength, and the like. Silicon carbide single crystal substrate 10 contains an n-type impurity such as nitrogen (N), for example. Silicon carbide single crystal substrate 10 has an n-type conductivity, for example. The first major surface 11 is, for example, a surface that is inclined by 8 ° or less from the {0001} plane or the {0001} plane. When the 1st main surface 11 inclines from {0001} surface, the inclination direction of the normal line of the 1st main surface 11 is <11-20> direction, for example.

  As shown in FIGS. 3 and 4, silicon carbide layer 20 is an epitaxial layer formed on silicon carbide single crystal substrate 10. Silicon carbide layer 20 is on first main surface 11. Silicon carbide layer 20 is in contact with first main surface 11. Silicon carbide layer 20 includes an n-type impurity such as nitrogen, for example. Silicon carbide layer 20 has an n conductivity type, for example. The concentration of n-type impurities contained in silicon carbide layer 20 may be lower than the concentration of n-type impurities contained in silicon carbide single crystal substrate 10. As shown in FIG. 1, the maximum diameter 111 (diameter) of the second major surface 30 is 100 mm or more. The diameter of the maximum diameter 111 may be 150 mm or more, 200 mm or more, or 250 mm or more. The upper limit of the maximum diameter 111 is not particularly limited. The upper limit of the maximum diameter 111 may be 300 mm, for example.

  Second main surface 30 may be, for example, a {0001} plane or a plane inclined by 8 ° or less from the {0001} plane. Specifically, the second main surface 30 may be a (0001) plane or a plane inclined by 8 ° or less from the (0001) plane. The inclination direction (off direction) of the normal line of second main surface 30 may be, for example, the <11-20> direction. The inclination angle (off angle) from the {0001} plane may be 1 ° or more, or 2 ° or more. The off angle may be 7 ° or less, or 6 ° or less.

  As shown in FIGS. 3 and 4, silicon carbide layer 20 has a buffer layer 21 and a drift layer 24. The concentration of the n-type impurity included in the drift layer 24 may be lower than the concentration of the n-type impurity included in the buffer layer 21. The drift layer 24 constitutes the second major surface 30. The buffer layer 21 constitutes the fourth major surface 14. Silicon carbide layer 20 has a thickness 113 of 5 μm or more. The thickness 113 may be 10 μm or more, or 15 μm or more.

  As shown in FIG. 2, linear orientation flat 5 is provided on silicon carbide layer 20 and silicon carbide single crystal substrate 10. Outer edge 34 of silicon carbide epitaxial substrate 100 includes arc portion 7 and linear orientation flat 5. The center of a circumscribed circle of a triangle formed by any three points on the arc portion 7 may be the center 35 of the second main surface 30.

  As shown in FIGS. 2 to 4, the silicon carbide layer 20 includes a central region 33, a first end region 31, a second end region 32, a third end region 36, and a fourth end region. 37. The central region 33 is in a position (fifth position) that is 2 μm away from the center 35 of the second main surface 30 toward the first main surface 11 in the direction perpendicular to the second main surface 30. In other words, the distance 121 from the fifth position to the second main surface 30 in the direction perpendicular to the second main surface 30 is 2 μm. The central region 33 is, for example, a region within 1 μm from the fifth position in each of a direction perpendicular to the second main surface 30 and a direction parallel to the second main surface 30. In the direction perpendicular to the second main surface 30, the distance from the second main surface 30 to the upper end surface of the central region 33 is, for example, 1 μm.

  As shown in FIGS. 2 and 3, the first end region 31 is located on the plane 3 that divides the orientation flat 5 into two equal parts when viewed from the direction perpendicular to the second main surface 30. And, it is in a position (first position) 1 mm away from the orientation flat 5 toward the central region 33. In other words, in the radial direction of the second main surface 30, the shortest distance 122 from the first position to the orientation flat 5 is 1 mm. The first position and the fifth position are on the plane 3. The plane 3 is parallel to the second direction 102, for example. The first end region 31 is, for example, a region within 1 μm from the first position in each of a direction perpendicular to the second main surface 30 and a direction parallel to the second main surface 30. In the direction perpendicular to the second main surface 30, the distance from the second main surface 30 to the upper end surface of the first end region 31 is, for example, 1 μm.

  As shown in FIGS. 2 and 4, the second end region 32 is a direction rotated in the circumferential direction 90 ° counterclockwise from the first end region 31 when viewed from the central region 33, and The silicon carbide layer 20 is located at a position (second position) 1 mm away from the outer edge 34 toward the central region 33. In other words, in the radial direction of the second main surface 30, the shortest distance 122 from the second position to the outer edge 34 is 1 mm. The fifth position and the second position are on the plane 4. The plane 4 is parallel to the first direction 101, for example. The plane 4 is perpendicular to the plane 3 and perpendicular to the second major surface 30. For example, the second end region 32 is a region within 1 μm from the second position in each of a direction perpendicular to the second main surface 30 and a direction parallel to the second main surface 30. In the direction perpendicular to the second main surface 30, the distance from the second main surface 30 to the upper end surface of the second end region 32 is, for example, 1 μm.

  As shown in FIGS. 2 and 3, the third end region 36 is located on the side opposite to the first end region 31 when viewed from the central region 33. The third end region 36 is a direction rotated 90 ° counterclockwise from the second end region 32 when viewed from the central region 33, and from the outer edge 34 of the silicon carbide layer 20 to the central region 33. It is in the position (3rd position) 1 mm away toward. The third position, the fifth position, and the first position are on the plane 3.

  As shown in FIGS. 2 and 4, the fourth end region 37 is located on the side opposite to the second end region 32 when viewed from the central region 33. The fourth end region 37 is a direction rotated counterclockwise by 90 ° from the third end region 36 when viewed from the central region 33, and from the outer edge 34 of the silicon carbide layer 20 to the central region 33. It is in the position (4th position) 1 mm away. The fourth position, the fifth position, and the fourth position are on the plane 4.

  As shown in FIG. 3, the distance 125 from the center 35 of the second main surface 30 to the orientation flat 5 may be shorter than the distance 126 from the center 35 to the arc portion 7. As shown in FIG. 4, the distance 123 from the center 35 to the arc portion 7 on one side may be the same as the distance 124 from the center 35 to the arc portion 7 on the other side.

(Dopant density ratio)
Silicon carbide layer 20 contains, for example, nitrogen as a dopant. According to the silicon carbide epitaxial substrate 100 according to the present disclosure, the dopant density in the first end region 31 and the dopant in the central region 33 with respect to the average value of the dopant density in the first end region 31 and the dopant density in the central region 33. The ratio of the absolute value of the difference from the density (first ratio) is 40% or less. Ratio of absolute value of difference between dopant density of second end region 32 and central region 33 with respect to average value of dopant density of second end region 32 and dopant density of central region 33 (second ratio) ) Is 40% or less. The first ratio may be 35% or less, 30% or less, 25% or less, or 20% or less. The second ratio may be 35% or less, 30% or less, 25% or less, or 20% or less.

The dopant density of the central region 33 and _{N dc,} the dopant density of the first end region 31 and _{N de1,} the dopant density of the second end region 32 and _{N de2,} the first ratio and R1, second When the ratio and _{R2, R1 = | N de1 -N} dc | a _{/ {(N de1 + N dc} ) / 2}, R2 = | N de2 -N dc | / with _{{(N de2 + N dc)} / 2} is there.

  Preferably, the ratio of the absolute value of the difference between the dopant density in the third end region 36 and the dopant density in the central region 33 to the average value of the dopant density in the third end region 36 and the dopant density in the central region 33 ( The third ratio) is 40% or less. Preferably, the ratio of the absolute value of the difference between the dopant density of the fourth end region 37 and the dopant density of the central region 33 to the average value of the dopant density of the fourth end region 37 and the dopant density of the central region 33 ( The fourth ratio) is 40% or less. The third ratio may be 35% or less, 30% or less, 25% or less, or 20% or less. The fourth ratio may be 35% or less, 30% or less, 25% or less, or 20% or less.

The dopant density of the central region 33 and _{N dc,} the dopant density of the third end region 36 and _{N de3,} the dopant density of the fourth end region 37 and _{N de4,} the third ratio and R3, fourth When the ratio of the _{R4, R3 = | N de3 -N} dc | a _{/ {(N de3 + N dc} ) / 2}, R4 = | N de4 -N dc | / with _{{(N de4 + N dc)} / 2} is there.

Next, a method for measuring the dopant density will be described. The dopant density in each region can be measured by, for example, SIMS (Secondary Ion Mass Spectrometry). As SIMS, IMS7f by Cameca can be used, for example. For example, the measurement conditions of primary ion O ₂ ⁺ and primary ion energy 8 keV can be used.

(Deposition system)
Next, the configuration of manufacturing apparatus 200 used in the method for manufacturing silicon carbide epitaxial substrate 100 according to the present embodiment will be described.

  As shown in FIG. 5, the manufacturing apparatus 200 is, for example, a hot wall type CVD (Chemical Vapor Deposition) apparatus. The manufacturing apparatus 200 mainly includes a heating element 203, a quartz tube 204, a heat insulating material 205, an induction heating coil 206, and a preheating mechanism 211. A cavity surrounded by the heating element 203 is a reaction chamber 201. Reaction chamber 201 is provided with a susceptor plate 210 that holds silicon carbide single crystal substrate 10. The susceptor plate 210 can rotate. Silicon carbide single crystal substrate 10 is placed on susceptor plate 210 with first main surface 11 facing up.

  The heating element 203 is made of, for example, graphite. The induction heating coil 206 is wound along the outer periphery of the quartz tube 204. By supplying a predetermined alternating current to the induction heating coil 206, the heating element 203 is induction heated. Thereby, the reaction chamber 201 is heated.

  The manufacturing apparatus 200 further includes a gas introduction port 207 and a gas exhaust port 208. The gas exhaust port 208 is connected to an exhaust pump (not shown). The arrows in FIG. 5 indicate the gas flow. Carrier gas, source gas and doping gas are introduced into the reaction chamber 201 through the gas inlet 207 and exhausted through the gas outlet 208. The pressure in the reaction chamber 201 is adjusted by the balance between the gas supply amount and the gas exhaust amount.

  Usually, the susceptor plate 210 and the single crystal substrate 10 are arranged at substantially the center in the axial direction of the reaction chamber 201. As shown in FIG. 5, in the present disclosure, the susceptor plate 210 and the single crystal substrate 10 may be disposed downstream of the center of the reaction chamber 201, that is, on the gas exhaust port 208 side. This is because the decomposition reaction of the source gas sufficiently proceeds until the source gas reaches the single crystal substrate 10. This is expected to make the C / Si ratio distribution uniform in the plane of the single crystal substrate 10.

(Rotating mechanism)
As illustrated in FIG. 6, the manufacturing apparatus 200 may further include an MFC (Mass Flow Controller) 53 and a gas supply source 54. The heating element 203 is provided with a recess 68. The recess 68 includes a bottom surface 62 and a side surface 67. A gas ejection hole 63 is provided on the bottom surface 62. The gas ejection hole 63 communicates with a flow path 64 provided in the heating element 203. The gas supply source 54 is configured to be able to supply a gas such as hydrogen to the flow path 64. An MFC 53 is provided between the gas supply source 54 and the flow path 64. The MFC 53 is configured to be able to control the flow rate of the gas supplied from the gas supply source 54 to the flow path 64. The gas supply source 54 is a gas cylinder capable of supplying an inert gas such as hydrogen or argon. The susceptor plate 210 is provided with a recess 73. The recess 73 includes a bottom surface 71 and a side surface 66. Silicon carbide single crystal substrate 10 can be arranged in recess 73.

  As shown in FIG. 7, the bottom surface 62 is provided with a plurality of gas ejection holes 63. When viewed from the direction perpendicular to the bottom surface 62, the gas ejection holes 63 may be provided at positions of 0 °, 90 °, 180 °, and 270 °, for example. Each of the plurality of gas ejection holes 63 is configured to eject gas along the circumferential direction of the bottom surface 61 of the susceptor plate 210. When viewed from a direction parallel to the bottom surface 62 (in the visual field of FIG. 6), the direction of the gas ejected from the gas ejection holes 63 may be inclined with respect to the bottom surface 61. 6 and 7, the direction of the arrow indicates the direction of gas flow. By injecting gas onto bottom surface 61, susceptor plate 210 floats and rotates in circumferential direction 103 of silicon carbide single crystal substrate 10. The susceptor plate 210 rotates in the circumferential direction 103 while the bottom surface 61 of the susceptor plate 210 is separated from the bottom surface 62 of the recess 68 and the outer surface 65 of the susceptor plate 210 is separated from the side surface 67 of the recess 68.

(Distance between outer edge of silicon carbide single crystal substrate and side surface of recess)
As shown in FIGS. 6 and 8, the side surface 66 of the recess 73 provided in the susceptor plate 210 includes a first portion 69 that is linear in a plan view and a second portion 70 that is curved in a plan view. Has been. First portion 69 is a portion that faces orientation flat 5 of silicon carbide single crystal substrate 10. Second portion 70 is a portion facing arc portion 7 of silicon carbide single crystal substrate 10. In a direction parallel to the bottom surface 61 of the susceptor plate 210, the distance 112 between the first portion 69 and the orientation flat 5 is 1 mm or less. Similarly, in the direction parallel to the bottom surface 61, the distance 116 between the second portion 70 and the arc portion 7 is 1 mm or less. Preferably, the distance between outer edge 34 and side surface 66 is 1 mm or less around the entire periphery of outer edge 34 of silicon carbide single crystal substrate 10. By shortening the distance between the outer edge 34 and the side surface 66 to about 1 mm or less, it is possible to prevent the source gas from entering between the outer edge 34 and the side surface 66 and disturbing the flow of the source gas. As a result, it is possible to suppress doping of more nitrogen in the outer peripheral region than in the central region of silicon carbide single crystal substrate 10.

(Distance between the outer surface of the susceptor plate and the side surface of the recess)
Heating element 203 and susceptor plate 210 are heated using induction heating coil 206. The temperature of the outer peripheral corner portion 74 of the susceptor plate 210 is higher than the temperature of the portion of the susceptor plate 210 other than the outer peripheral corner portion 74. As shown in FIG. 6, the outer peripheral corner portion 74 of the susceptor plate 210 is a contact point between the outer surface 65 and the flat portion 72. In the susceptor plate 210, the temperature of the outer peripheral corner portion 74 is the highest. Therefore, when the distance between outer peripheral corner portion 74 and silicon carbide single crystal substrate 10 is short, the temperature of the outer peripheral region of silicon carbide single crystal substrate 10 becomes higher than the temperature of the central region. As a result, more nitrogen is doped in the outer peripheral region than in the central region of silicon carbide single crystal substrate 10. Therefore, it is desirable that the distance between silicon carbide single crystal substrate 10 and outer peripheral corner portion 74 of susceptor plate 210 is longer.

  Specifically, in a direction parallel to the bottom surface 61, a distance 119 between the side surface 66 of the recess 73 provided in the susceptor plate 210 and the outer peripheral corner portion 74 of the susceptor plate 210 is, for example, 20 mm or more (see FIG. 6 and FIG. 8). In other words, the width of the flat portion 72 of the susceptor plate 210 is 20 mm or more. As shown in FIG. 8, the distance 119 between the first portion 69 and the outer peripheral corner portion 74 may be 20 mm or more in the radial direction. Similarly, in the radial direction, the distance 117 between the second portion 70 and the outer peripheral corner portion 74 may be 20 mm or more. Preferably, the width of the flat portion 72 is 20 mm or more around the entire periphery of the susceptor plate 210.

  As shown in FIG. 9, the susceptor plate 210 may be provided with a plurality of recesses 73. Although the number of the recessed parts 73 is not specifically limited, For example, it is three. The first portion 69 of the side surface 66 of the recess 73 may be parallel to the tangent line of the outer surface 65 that faces the concave portion 73. The first portion 69 may be located on the outer surface 65 side of the susceptor plate 210, and the second portion 70 may be located on the center side of the susceptor plate 210. Preferably, in the direction parallel to the bottom surface 61, the distance 118 between the two recesses 73 is 20 mm or more. Preferably, in a direction parallel to the bottom surface 61, the distance 119 between the first portion 69 and the outer surface 65 is 20 mm or more.

(Distance between the surface of the silicon carbide single crystal substrate and the flat portion of the susceptor plate)
When the thickness of silicon carbide single crystal substrate 10 is smaller than depth 115 of recess 73 provided in susceptor plate 210, the flow of the source gas on silicon carbide single crystal substrate 10 is disturbed. Therefore, the thickness of silicon carbide single crystal substrate 10 is desirably larger than depth 115 of recess 73. That is, the flat portion 72 is located between the first main surface 11 and the third main surface 13 in the direction perpendicular to the first main surface 11. Specifically, the distance 114 between the first main surface 11 and the flat portion 72 in the direction perpendicular to the first main surface 11 is, for example, 100 μm or less. For example, when depth 115 of recess 73 is 300 μm and thickness of silicon carbide single crystal substrate 10 is 350 μm, distance 114 is 50 μm. Thereby, it can suppress effectively that the flow of source gas is disturbed on a silicon carbide single crystal substrate.

(Preheating mechanism)
It is desirable that ammonia gas, which is a dopant gas, be sufficiently heated and thermally decomposed in advance before being supplied to the reaction chamber 201. Thereby, in the silicon carbide layer 20, it can be expected that the in-plane uniformity of the nitrogen (dopant) density is improved. As shown in FIG. 5, a preheating mechanism 211 is provided on the upstream side of the reaction chamber 201. In the preheating mechanism 211, the ammonia gas can be heated in advance. The preheating mechanism 211 includes a room heated to, for example, 1300 ° C. or higher. The ammonia gas is sufficiently thermally decomposed when passing through the inside of the preheating mechanism 211 and then supplied to the reaction chamber 201. With such a configuration, ammonia gas can be thermally decomposed without causing a large disturbance in the gas flow.

  The temperature of the inner wall surface of the preheating mechanism 211 is more preferably 1350 ° C. or higher. This is to promote thermal decomposition of ammonia gas. In consideration of thermal efficiency, the temperature of the inner wall surface of the preheating mechanism 211 is preferably 1600 ° C. or lower. The preheating mechanism 211 may be integrated with the reaction chamber 201 or may be a separate body. Further, the gas passing through the inside of the preheating mechanism 211 may be only ammonia gas or may contain other gases. For example, the entire source gas may be passed through the preheating mechanism 211.

(Method for producing silicon carbide epitaxial substrate)
Next, a method for manufacturing the silicon carbide epitaxial substrate according to this embodiment will be described.

  First, a polytype 6H silicon carbide single crystal is manufactured by, for example, a sublimation method. Next, silicon carbide single crystal substrate 10 is prepared by slicing the silicon carbide single crystal with, for example, a wire saw. Silicon carbide single crystal substrate 10 has a first main surface 11 and a third main surface 13 opposite to first main surface 11. The first main surface 11 is a surface inclined by, for example, 8 ° or less from the {0001} plane. As shown in FIGS. 5 and 6, silicon carbide single crystal substrate 10 is arranged in recess 73 of susceptor plate 210 such that first main surface 11 is exposed from susceptor plate 210. Specifically, silicon carbide single crystal substrate 10 is arranged such that flat portion 72 is located between first main surface 11 and third main surface 13 in the direction perpendicular to first main surface 11. Arranged in the recess 73. In a direction perpendicular to the first main surface 11, the distance 114 between the first main surface 11 and the flat portion 72 is, for example, 100 μm or less. Next, silicon carbide layer 20 is formed by epitaxial growth on silicon carbide single crystal substrate 10 using manufacturing apparatus 200 described above.

For example, after the pressure in the reaction chamber 201 is reduced from atmospheric pressure to about 1 × 10 ⁻⁶ Pa, the temperature rise of the silicon carbide single crystal substrate 10 is started. During the temperature increase, hydrogen (H ₂ ) gas that is a carrier gas is introduced into the reaction chamber 201.

After the temperature in the reaction chamber 201 reaches, for example, about 1600 ° C., the source gas and the doping gas are introduced into the reaction chamber 201. The source gas includes a Si source gas and a C source gas. For example, silane (SiH ₄ ) gas can be used as the Si source gas. As the C source gas, for example, propane (C ₃ H ₈ ) gas can be used. The flow rate of silane gas and the flow rate of propane gas are, for example, 46 sccm and 14 sccm. The volume ratio of silane gas to hydrogen is, for example, 0.04%. The C / Si ratio of the source gas is, for example, 0.9.

As the doping gas, for example, ammonia (NH ₃ ) gas is used. Ammonia gas is more easily pyrolyzed than nitrogen gas having a triple bond. By using ammonia gas, improvement in the in-plane uniformity of the carrier concentration can be expected. The concentration of ammonia gas relative to hydrogen gas is, for example, 1 ppm. Before the ammonia gas is introduced into the reaction chamber 201, it is desirable that it be thermally decomposed in advance by the preheating mechanism 211. The ammonia gas is heated to, for example, 1300 ° C. or more by the preheating mechanism 211.

  The silicon carbide layer 20 is epitaxially grown on the silicon carbide single crystal substrate 10 by introducing the carrier gas, the source gas and the doping gas into the reaction chamber 201 in a state where the silicon carbide single crystal substrate 10 is heated to about 1600 ° C. It is formed by. While the silicon carbide layer 20 is epitaxially grown, the susceptor plate 210 rotates around the rotation shaft 212 (see FIG. 5). The average rotational speed of the susceptor plate 210 is, for example, 20 rpm. Thus, silicon carbide layer 20 is formed on silicon carbide single crystal substrate 10 by epitaxial growth.

(Method for manufacturing silicon carbide semiconductor device)
Next, a method for manufacturing the silicon carbide semiconductor device 300 according to this embodiment will be described.

  The method for manufacturing a silicon carbide semiconductor device according to the present embodiment mainly includes an epitaxial substrate preparation step (S10: FIG. 10) and a substrate processing step (S20: FIG. 10).

  First, an epitaxial substrate preparation step (S10: FIG. 10) is performed. Specifically, silicon carbide epitaxial substrate 100 is prepared by the above-described method for manufacturing a silicon carbide epitaxial substrate (see FIG. 1).

  Next, a substrate processing step (S20: FIG. 10) is performed. Specifically, a silicon carbide semiconductor device is manufactured by processing a silicon carbide epitaxial substrate. “Processing” includes, for example, various processes such as ion implantation, heat treatment, etching, oxide film formation, electrode formation, and dicing. That is, the substrate processing step may include at least one of ion implantation, heat treatment, etching, oxide film formation, electrode formation, and dicing.

  Below, the manufacturing method of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as an example of a silicon carbide semiconductor device is demonstrated. The substrate processing step (S20: FIG. 10) includes an ion implantation step (S21: FIG. 10), an oxide film formation step (S22: FIG. 10), an electrode formation step (S23: FIG. 10), and a dicing step (S24: FIG. 10). including.

  First, an ion implantation step (S21: FIG. 10) is performed. A p-type impurity such as aluminum (Al) is implanted into second main surface 30 on which a mask (not shown) having an opening is formed. Thereby, body region 132 having p-type conductivity is formed. Next, an n-type impurity such as phosphorus (P) is implanted into a predetermined position in body region 132. Thereby, a source region 133 having n-type conductivity is formed. Next, a p-type impurity such as aluminum is implanted into a predetermined position in the source region 133. As a result, a contact region 134 having a p-type conductivity is formed (see FIG. 11).

  In silicon carbide layer 20, portions other than body region 132, source region 133, and contact region 134 serve as drift region 131. Source region 133 is separated from drift region 131 by body region 132. Ion implantation may be performed by heating silicon carbide epitaxial substrate 100 to about 300 ° C. or more and 600 ° C. or less. After the ion implantation, activation annealing is performed on silicon carbide epitaxial substrate 100. By the activation annealing, the impurities injected into the silicon carbide layer 20 are activated, and carriers are generated in each region. The atmosphere of activation annealing may be, for example, an argon (Ar) atmosphere. The activation annealing temperature may be about 1800 ° C., for example. The activation annealing time may be about 30 minutes, for example.

Next, an oxide film forming step (S22: FIG. 10) is performed. For example, silicon carbide epitaxial substrate 100 is heated in an atmosphere containing oxygen, whereby oxide film 136 is formed on second main surface 30 (see FIG. 12). Oxide film 136 is made of, for example, silicon dioxide (SiO ₂ ). The oxide film 136 functions as a gate insulating film. The temperature of the thermal oxidation treatment may be about 1300 ° C., for example. The thermal oxidation treatment time may be about 30 minutes, for example.

After the oxide film 136 is formed, heat treatment may be performed in a nitrogen atmosphere. For example, the heat treatment may be performed at about 1100 ° C. for about 1 hour in an atmosphere such as nitric oxide (NO) or nitrous oxide (N ₂ O). Thereafter, heat treatment may be performed in an argon atmosphere. For example, the heat treatment may be performed in an argon atmosphere at about 1100 to 1500 ° C. for about 1 hour.

  Next, an electrode formation step (S23: FIG. 10) is performed. The first electrode 141 is formed on the oxide film 136. The first electrode 141 functions as a gate electrode. The first electrode 141 is formed by, for example, a CVD method. The first electrode 141 is made of, for example, polysilicon containing impurities and having conductivity. The first electrode 141 is formed at a position facing the source region 133 and the body region 132.

  Next, an interlayer insulating film 137 that covers the first electrode 141 is formed. Interlayer insulating film 137 is formed by, for example, a CVD method. Interlayer insulating film 137 is made of, for example, silicon dioxide. The interlayer insulating film 137 is formed so as to be in contact with the first electrode 141 and the oxide film 136. Next, the oxide film 136 and the interlayer insulating film 137 at predetermined positions are removed by etching. As a result, the source region 133 and the contact region 134 are exposed from the oxide film 136.

  For example, the second electrode 142 is formed on the exposed portion by a sputtering method. The second electrode 142 functions as a source electrode. Second electrode 142 is made of, for example, titanium, aluminum, silicon, or the like. After second electrode 142 is formed, second electrode 142 and silicon carbide epitaxial substrate 100 are heated at a temperature of about 900 to 1100 ° C., for example. Thereby, second electrode 142 and silicon carbide epitaxial substrate 100 come into ohmic contact. Next, the wiring layer 138 is formed so as to be in contact with the second electrode 142. The wiring layer 138 is made of a material containing aluminum, for example.

  Next, the third electrode 143 is formed on the third main surface 13. The third electrode 143 functions as a drain electrode. Third electrode 143 is made of, for example, an alloy containing nickel and silicon (eg, NiSi).

  Next, a dicing step (S24: FIG. 10) is performed. For example, silicon carbide epitaxial substrate 100 is diced along a dicing line, whereby silicon carbide epitaxial substrate 100 is divided into a plurality of semiconductor chips. From the above, silicon carbide semiconductor device 300 is manufactured (see FIG. 13).

  In the above, the manufacturing method of the silicon carbide semiconductor device according to the present disclosure has been described by exemplifying the MOSFET, but the manufacturing method according to the present disclosure is not limited to this. The manufacturing method according to the present disclosure can be applied to various silicon carbide semiconductor devices such as IGBT (Insulated Gate Bipolar Transistor), SBD (Schottky Barrier Diode), thyristor, GTO (Gate Turn Off Thyristor), and PiN diode.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

  3, 4 plane, 5 orientation flat, 7 arc portion, 10 silicon carbide single crystal substrate, 11 first main surface, 13 third main surface, 14 fourth main surface (surface), 20 silicon carbide layer, 21 buffer layer, 24 drift layer, 30 second main surface, 31 first end region, 32 second end region, 33 central region, 34 outer edge, 35 center, 36 third end region, 37 fourth end region, 53 MFC , 54 Gas supply source, 61, 62, 71 bottom surface, 63 gas ejection hole, 64 flow path, 65 outer side surface, 66, 67 side surface, 68, 73 recess, 69 first part, 70 second part, 72 flat part, 74 peripheral corner, 100 silicon carbide epitaxial substrate, 101 first direction, 102 second direction, 103 peripheral direction, 111 maximum diameter, 122 shortest distance, 131 drift region, 132 body region, 1 33 source region, 134 contact region, 136 oxide film, 137 interlayer insulating film, 138 wiring layer, 141 first electrode, 142 second electrode, 143 third electrode, 200 manufacturing apparatus, 201 reaction chamber, 203 heating element, 204 quartz Pipe, 205 heat insulating material, 206 induction heating coil, 207 gas introduction port, 208 gas exhaust port, 210 susceptor plate, 211 preheating mechanism, 212 rotating shaft, 300 silicon carbide semiconductor device.

Claims (10)

A silicon carbide single crystal substrate including a first main surface;
A silicon carbide layer on the first main surface,
The silicon carbide layer includes a second main surface opposite to a surface in contact with the silicon carbide single crystal substrate,
The maximum diameter of the second main surface is 100 mm or more,
The silicon carbide single crystal substrate and the silicon carbide layer are provided with a linear orientation flat,
The silicon carbide layer has a central region, a first end region, and a second end region,
The central region is at a position 2 μm away from the center of the second main surface toward the first main surface in a direction perpendicular to the second main surface,
The first end region is located on a plane that bisects the orientation flat vertically when viewed from a direction perpendicular to the second main surface, and from the second main surface to the first main surface. 2 μm away from the orientation flat and 1 mm away from the orientation flat toward the central region,
The second end region is a direction rotated counterclockwise by 90 ° from the first end region, as viewed from the central region, from the second main surface to the first main surface. 2 μm away from the outer edge of the silicon carbide layer and 1 mm away from the outer edge of the silicon carbide layer toward the central region,
The first ratio of the absolute value of the difference between the dopant density of the first end region and the dopant density of the central region with respect to the average value of the dopant density of the first end region and the dopant density of the central region is: Absolute difference between the dopant density of the second end region and the dopant density of the central region with respect to the average value of the dopant density of the second end region and the dopant density of the central region. The silicon carbide epitaxial substrate whose 2nd ratio of a value is 40% or less.   The silicon carbide epitaxial substrate according to claim 1, wherein the first ratio is 30% or less.   The silicon carbide epitaxial substrate according to claim 2, wherein the first ratio is 20% or less.   The silicon carbide epitaxial substrate according to any one of claims 1 to 3, wherein the second ratio is 30% or less.   The silicon carbide epitaxial substrate according to claim 4, wherein the second ratio is 20% or less.   The silicon carbide epitaxial substrate according to claim 1, wherein the maximum diameter is 150 mm or more. Preparing the silicon carbide epitaxial substrate according to any one of claims 1 to 6,
A process for processing the silicon carbide epitaxial substrate. Placing the silicon carbide single crystal substrate in the recess of the susceptor plate;
After the step of disposing the silicon carbide single crystal substrate in the recess of the susceptor plate, a step of forming a silicon carbide layer on the silicon carbide single crystal substrate by epitaxial growth,
The outer edge of the silicon carbide single crystal substrate has an orientation flat and an arc portion connected to the orientation flat,
The side surface of the recess is composed of a first portion facing the orientation flat and a second portion facing the arc portion,
The distance between the first portion and the orientation flat is at 1mm or less, and the distance between the second portion and the arcuate portion is state, and are less 1mm,
In the radial direction, the distance between the outer peripheral corner portion of the susceptor plate and the first portion is 20 mm or more, and the distance between the outer peripheral corner portion and the second portion is 20 mm or more,
In the step of forming a silicon carbide layer on the silicon carbide single crystal substrate by epitaxial growth, the susceptor plate rotates in a circumferential direction of the silicon carbide single crystal substrate, and ammonia gas is used as a doping gas. A method for manufacturing a substrate.   The method for manufacturing a silicon carbide epitaxial substrate according to claim 8, wherein a distance between the outer edge and the side surface is 1 mm or less around the entire periphery of the outer edge.   The thickness of the said silicon carbide single crystal substrate is a manufacturing method of the silicon carbide epitaxial substrate of Claim 8 or Claim 9 larger than the depth of the said recessed part.

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